1. Field of the Invention
This invention pertains to finishes containing agents specifically designed to render the materials treated therewith flame retardant.
2. Description of the Prior Art
Recent years have witnessed a great interest in and a growing demand for flame retardant textiles and fabrics. Due to its substantial portion of the textile market, one such fabric which has engrossed the attention of many is polyester/cotton blends. The market dominance of these blends is due in part to consumers' demand for minimum care products of satisfactory overall performance and wear-life. However, polyester/cotton blend fabrics have persisted in evading researchers in their attempts to successfully impart durable flame retardancy to them without a loss of or significant dimunition in their physical properties. For example, although satisfactory flame retardants are available for 100% cotton fabrics and 100% polyester fabrics, satisfactory flame retardants have not hitherto been available for polyester/cotton blend fabrics. This phenomena is in part due to the fact that "(c)hemical systems which have been developed for flame retardant finishing of 100% cellulosics are not necessarily effective in imparting self-extinguishing behavior to fabrics containing cellulosic and polyester fibers." G. C. Tesoro, "Status and Prospects for Flame Resistant Polyester/Cellulose Blend Fabrics," 39, National Technical Information Service, Springfield, VA, 1973. Also, "(t)here are significant differences in the extent to which organophosphorus systems found to be effective flame retardants for cellulose maintain this effectiveness in the presence of polyester." Ibid., 39. Additionally, "(t)he synergistic contribution of nitrogen to flame retardant effectiveness of phosphorus (which has been documented for 100% cellulose substrates) has not been demonstrated as being significant in the presence of polyester." Ibid., 39.
A news release by the Textile Research Institute, Princeton, New Jersey for release not before Mar. 2, 1975, entitled "TRI Studies on Flame Retardancy of Polyester/Cotton Blends," reports that "one of the major problems with polyester/cotton blends is that the flammability behavior of these blends cannot be directly predicted from the behavior of the components. For example, the study at TRI has revealed that such blends ignite sooner, burn faster, generate heat faster, and thermally decompose faster than might be expected on the basis of the behavior of cotton and of polyester alone. The data indicate that there are important interactions between the cotton and the polyester when these two fibers are burned in combination. -- (F)or example, -- mixtures of polyester and cotton evolve more volatile hydrocarbons, such as ethylene and acetylene, than are evolved by cotton and by polyester when these fibers are pyrolyzed alone under comparable conditions. This is one of the reasons that the blends are difficult to flame retard." This report concludes that "(a) blend becomes a new chemical species with its own unique flammability properties."
In "Progress in the Development of Flame-Resistant Polyester-Cotton Blends", Proceedings of the 1974 Symposium on Textile Flammability, 116, LeBlanc Research Corporation, 5454 Post Road, East Greenwich, Rhode Island, 1974, W. A. Reeves et al. state that "(s)atisfactory flame retardants are available for cotton fabrics and polyester fabrics but are not available for polyester/cotton blend fabrics". Although "(s)ome flame retardants for cellulosic fibers are equally effective on polyester and vice versa if one is only interested in flame resistance", "(p)roperties such as aesthetics and durability to laundering are often lacking in treated fabrics."
Vladimir Mischutin in an article entitled "A New FR System for Synthetic/Cellulosic Blends", Textile Chemist and Colorist, Vol. 7, No. 3, pp 40/2 (March, 1975) reports that "(s)ince the passage in 1967 of the amendment to the 1953 Flammable Fabrics Act, textile researchers have sought to develop technology to produce flame retardant fabrics. This has resulted in the development of various commercial processes to render 100% cotton fabrics flame retardant. In addition, a FR process involving emulsion containing tris(dibromopropyl)phosphate was developed for 100% polyester fabrics. This technology, together with the use of inherently flame retardant fibers, was sufficient to satisfy the requirements for sleepwear in sizes 0-6X; however, the intent of the law was not limited to the sleepwear worn by children. Additional technology was needed to satisfy growing demand for flame retardant fabrics.
"Initially, it appeared a simple matter to combine the available techinques for cellulosic fabrics and for polyester goods and obtain flame retardant blends, which are by far the biggest volume used for apparel. Those that tried this approach were unpleasantly surprised. Existing technology did not answer the requirement on blends, and new techniques were needed.
"Among brominated flame retardants the material most commonly used is tris(2,3-dibromopropyl)phosphate. This material possesses good heat and hydrolytic stabilities; it is highly insoluble in water; it is colorless and nontoxic. However, tris(dibromopropyl)phosphate is a secondary plasticizer and has a tendency to impact (sic) a tacky hand to the substrates to which it is applied. In addition, due to its lack of reactive groups, it is difficult to attach permanently to both synthetic and cellulosic fibers. In view of this, all efforts to obtain a flame retardant system for polyester/cellulosic fabric which would comply with DOC FF 3-71 were completely unsuccessful."
Similarly, Dr. W. F. Battinger states in "The Application of a Phosphonium Salt Flame Retardant to Polyester-Cotton Blend Fabrics," Book of Papers, 1974 National Technical Conference, (Oct. 9 to the 11, 1974, New Orleans, Louisianna), 467, American Association of Textile Chemists and Colorists, P.O. Box 12215, Research Triangle Park, N.C. 27709, 1974, that "the treatment of polyester/cotton blends presents a difficult problem in flammability protection because of the vast differences in physical properties and burning characteristics between two fibers". In this paper, Dr. Battinger reports the results of his research with combination applications of phosphonium salts, urea and tris(2,3-dibromopropyl)phosphate in the following words:
"The lowered response of LOI to added phosphorus for a blend fabric compared to 100% cotton is indicative of major differences in flammability protective mechanisms for the two fibers. Since the phosphonium salt studied here in only marginally capable of protecting the blend utilizing phosphorus and nitrogen alone, consideration of phosphorus and bromine in combination is a viable alternative. Tris-2,3-dibromopropyl phosphate was chosen as a bromine source because of its ready availability and known activity in improving 100% polyester fabric flammability characteristics. Since the LOI/%P responses for the 50/50 and 65/35 polyester/cotton blend were similar (with respect to the same add-on levels of tetrakis-(hydroxymethyl)phosphonium oxalate), the 65/35 blend is used to illustrate the combination effect. -- The dibromopropyl phosphate in perchloroethylene was padded onto the fabric, followed by drying and curing 1.5 minutes at 400.degree. F. to simulate Thermosoling. The process wash consisted of one Kenmore wash with detergent. -- (F)ixation as judged by durability of this wash was quite good. Maximum OI values of 0.24 were obtained at about 10% Br applied. From related studies on 100% cotton for this material showing lesser durability, it can be inferred that most of the bromine containing material is associated with the polyester component of the blend. (Note: This is the converse of what applied for the phosphonium salt previously.)
"The identical fabrics used to generate these curves were then subjected to an aqueous application of tetrakis-hydroxymethyl phosphonium oxalate in the same fashion as the blends were treated previously. Applications were set to provide 2% phosphorus. This value was chosen to theoretically yield an increase of 0.05 OI unit. The consequences of the topical application -- compared to theoretical calculations show excellent agreement indicating the additivity properties of LOI data. Somewhat surprisingly, however, while LOI values of 0.29 were attained, no samples passes the DOC vertical test.
"The anomaly of materials with LOI's of 25 passing the vertical test when phosphonium compounds alone were employed, and LOI's of 29 failing when a supplemental bromine compound is used is reconcilable in part by consideration of the action of the materials as flame retardants and the geometry of the test employed. The phosphonium compound is a "condensed phase" acting flame retardant; no evidence is available indicating its action in vapor phase chemistry, nor is it a melt-decomposition temperature reducer for polyester. Dibromopropyl phosphate, on the other hand, is known to significantly lower the melt decomposition temperature of polyester fiber. For 100% polyester fabrics, flame retardancy is enhanced by this shrinking and dripping away. In a blend with cellulose, however, this cannot occur because of the support provided by the cotton, thus the geometry of burning comes into play. In the LOI test the sample is burned vertically downward; as polyester melts, it flows from the flame front, thus depleting fuel supply. In the DOC test burning is vertically upward and the reverse effect, fuel enrichment, occurs. The net results of these effects logically seems exactly what was observed in these experiments-- high LOI's but failures in DOC testing."
Concern has begun to mount as to whether polyester/cotton blend fabrics will lose their share of the textile market because of present, pending, and contemplated federal and state legislation mandating non-flammability standards for, inter alia, fabrics and textiles. A clear example of this concern can be seen in the following excerpt wherein the authors argue for the lowering of the flammability standard for polyester/cotton blend fabrics:
"The types of fabric used in largest volume for apparel are polyester/cotton blends. At present there is no fully commercial method of producing polyester/cotton fabric to meet FF 3-71, primarily because of problems with the hand of the treated fabrics. Obviously, if there is any extension of standards requiring self-extinguishing properties beyond the present small end-uses (children's sleepwear), the peculiarities of this blend will have to be considered.
"The importance of a standard that is no more restrictive then is necessary to get the maximum reasonable safety under realistic use situations is particularly important for polyester/cotton blend fabrics. These fabrics comprise the major portion of apparel fabrics. They also are the types of fabrics which are the most difficult to flame retard to meet FF 3-71 and retain acceptable esthetics.
"We have been able to produce cellulosic fabrics, polyester fabrics acetate fabrics, modacrylics, blends of thermoplastic fibers, etc. to meet FF 3-71. Flame retardant polyester/cotton durable press fabrics meeting FF 3-71 have not been produced by a commercially viable process.
"The key technical problem is `hand` of the treated fabrics. The hand of treated fabrics is objectionally stiff because of the necessity of using inordinately high add-ons of chemicals to pass FF 3-71. The modified test methods we have discussed would allow for much lower add-ons of chemicals to be used which would give a more acceptable hand to the treated fabrics. This would also lower the chemical cost of the finish.
"Many apparel items-- such as jackets, girls' dresses, hats, bathrobes, topcoats, etc.-- may not be laundered 50 times during their life. Standards for apparel by end-use which require less extensive laundering would also allow for lower chemical add-ons to be used.
"A reasonable test method for polyester/cotton apparel fabrics should be developed as soon as possible so that FF 3-71 will not be adopted when new, more restrictive apparel standards may be required in the future." R. B. LeBlanc and D. A. LeBlanc, "Future Flammability Standards for Apparel: Can They Be Reasonable and Practical, Too?," Textile Chemist and Colorist, Vol. 7, No. 5, 56/17 (April, 1975).
It has been discovered that novel flame retardant finishes are capable of rendering textile materials, including polyester/cotton blend fabrics, treated therewith flame retardant, i.e., capable of passing the U.S. Department of Commerce FF 3-71 flammability test. The flame retardant finishes of this invention impart durable flame retardancy as well as ease of care properties to fabrics and textiles treated therewith without significantly detrimentally affecting the hand of the treated fabrics and textiles.